The average quality of crude oil produced worldwide is becoming heavier (higher density/more carbon rich) and sourer (higher in sulphur) as the light sweet crude oil fields are depleting. Heavy-sour crudes contain high concentrations of metals such as vanadium and nickel. The concentration of metals in crude oil can vary from a few ppm up to 1,000 ppm; the vanadium to nickel ratio is typically 6:1.
Deep conversion processes (e.g. coking, flexicoking, visbreaking, gasification etc.) and sulphur removal processes are required to break down the heavy products into lighter products. The heavier and sourer the crude oil, the more extensive and expensive the cracking and sulphur removal processes become.
The metal content of oil refinery residues is an increasing environmental concern. Vanadium is a known mutagen, and nickel a known carcinogen; the release of these metals to the environment is becoming increasingly tightly monitored and controlled by Environment Agencies worldwide.
Existing disposal routes for refinery residues with high sulphur and metals contents are under increasing pressure as the environmental liability for removal of metals from the processing of the waste streams, e.g. from flue gases following power generation, make the processing unviable. Other disposal routes such as landfill are also becoming more limited in availability and increasingly costly.
Catalysts have been used widely in the refining and chemical processing industries for many years. Hydroprocessing catalysts, including hydrotreating and hydrocracking catalysts, are now widely employed in facilities worldwide. These hydroprocessing catalysts typically produce increased yields, faster reaction times, and improved product properties when compared with pri- or (non-catalytic) thermal processes for converting crude oils into refined products.
Hydroprocessing catalysts typically employed in commercial application today are classified as “supported” catalysts. These catalyst supports, which are generally molecular sieves such as SAPO's or zeolites, are often composed of materials such as silica, alumina, zirconia, clay, or some hybrid of these. A more expensive material, which imparts much of the actual catalytic activity, is impregnated on the support. These catalytic materials typically include metals such as nickel, molybdenum, and cobalt. In some cases platinum, palladium, and tungsten may be used.
Recently, a new generation of hydroprocessing catalysts has emerged. These catalysts do not require a support material. The catalyst is instead comprised of unsupported, micron-sited catalyst particles, such as molybdenum sulphide or nickel sulphide. These catalysts, due to factors such as increased surface area and other factors not discussed here, are many times more active than traditional supported catalysts. Performance is greatly improved during conversion operations when compared to traditional supported catalysts. One area in which these highly active, unsupported catalysts are currently being employed is vacuum residue hydrocracking. In the process of being utilized in residue hydrocracking service, these unsupported catalysts often suffer a high amount of metals (specifically vanadium) and coke deposition, which increases the need for fresh makeup catalyst.
One drawback to both supported and unsupported catalysts is their cost. Typically, replacement costs for an expensive noble metal catalyst may be a major operating expenditure item in a refinery or chemical plant. A market has thus emerged to reclaim spent catalysts, and specifically spent hydroprocessing catalysts, so that the valuable metals can be recycled. The current high price of various metals has driven this need even further. Several spent catalyst reclaimers are currently in business at various locations around the world. Unfortunately, however, these roasting (or pyrometallurgical) based reclaimers are designed to recover metals from supported catalysts.
Due to the high concentrations of metals, specifically molybdenum and nickel, used in this new generation of unsupported catalysts, a need has been identified for an economical unsupported catalyst metals recovery process. We have developed a novel process to recover these metals from this class of highly active, unsupported, catalysts, which are composed primarily of MoS2 or NiS. This process allows recovery of both the catalytic metals, including molybdenum and nickel, as well as the deposited metals, such as vanadium and nickel.
Means for recovery of vanadium, nickel and molybdenum from catalysts has been disclosed in other patents. For example, U.S. Pat. No. 4,762,812 discloses a process for the recovery of a spent supported catalyst comprising molybdenum sulphide from a hydroprocess for the upgrading of a hydrocarbonaceous mineral oil containing nickel and vanadium. The catalyst is further treated to remove molybdenum. The process preferentially recovers molybdenum, while leaving much of the vanadium in the catalyst.
U.S. Pat. No. 4,544,533 discloses a method for recovering metals from spent supported hydroprocessing catalyst. Metals recovered may be those obtained from crude oils, including iron, nickel, vanadium and tungsten as well as catalytic metals such as molybdenum, cobalt, or nickel. The catalyst is roasted to remove carbonaceous and sulphurous residues then metals are leached simultaneously from spent catalyst.
U.S. Pat. No. 4,514,369 discloses leaching spent supported catalysts, to obtain a liquor containing cobalt, nickel, molybdenum and vanadium. The metals are extracted, isolated and purified by liquid/liquid extraction techniques.
U.S. Pat. No. 4,432,949 discloses leaching metals from a catalytic support which had been previously roasted. Vanadium is removed by precipitation, and nickel, cobalt and molybdenum are then removed by serial ion exchange.